| Title | Subsurface characterization of the southern fringes of the Hellisheidi-Hverahlíd geothermal systems: Deep slim-well exploration drilling campaign. |
|---|---|
| Authors | Dario I. Di Rienzo, Ásdís Benediktsdóttir, Bjarni R. Kristjánsson, Thráinn Fridriksson |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | The Hellisheidi-Hverahlíd geothermal systems are situated within the Hengill central volcano in southwest Iceland. The fields have been extensively developed over the last two decades and today account for a generation capacity of 303 MWe and 210 MWth for district heating in Reykjavík, making it Europe’s largest geothermal plant on a single site. Reykjavík Energy and ON Power’s mandate for increased power production has set the focus for the next years on the exploration of the southern fringes of the producing fields, specifically the areas of Gráuhnúkar-Meitlar and Nordurhálsar. Surface exploration has been completed and an updated 3D resistivity model shows several shallow low-resistivity anomalies extending further south from the currently producing geothermal reservoirs. No surface manifestations are present in the Meitlar area and could thus represent a relatively young, fully sealed and hidden system at depth. The Gráuhnúkar-Meitlar area shows resistivity anomalies following the NE-SW structural trend of the Western Volcanic Zone and the Nordurhálsar plateau shows a narrower N-S trending anomaly. Deep slim wells (>1500mTD) will be drilled for the first time and although not intended for production, these wells will offer a cost-effective and less invasive means of acquiring subsurface data and will be strategically sited to test resistivity-temperature correlation. The goal is to provide valuable inputs for resource capacity estimates for future drilling strategies. Subsurface characterization through geological-geophysical logs, geochemical samples of geothermal fluids and well completion testing will play a pivotal role in supporting decision-making in sustainable field development by reducing uncertainty in resource delineation. |